AIKIDO-2026-352802
matrix-synapse is vulnerable to Improper Input Validation
5
Low Risk
This Affects:
matrix-synapseTL;DR
On some endpoints, Synapse accepts extraneous trailing suffix data on the request path. When a reverse proxy normalises paths for routing (for example converting /a/../b to /b), the differing interpretation between the proxy and Synapse can bypass reverse-proxy routing rules and expose unintended endpoints. Because sensitive endpoints such as Admin APIs still require a valid access token, this is a loss of defence in depth rather than a directly exploitable flaw. The fix stops Synapse from accepting the extraneous suffix data.
Who does this affect?
You are affected if you are using a version that falls within the vulnerable range and you rely on a reverse proxy that normalises request paths to restrict access to endpoints.
Background info
matrix-synapse is vulnerable to Improper Input Validation in versions 0.0.1 - 1.157.1.
How to fix this
Upgrade the matrix-synapse library to the patch version.
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